Car Overheating And No Heat

heater core with external heater hoses

I would like a little information on why my car engine is over heating and when it does I noticed there is no heat coming from the heater ducts as well.  What is causing this to happen?

Great question, and I am so glad you have also been able to determine another symptom that is happening…no heat from the heater.  This helps me narrow things down a bit.

If there is no hot air coming from the heater it is usually do to no hot coolant circulating in the engine. So if you have no hot heater air AND you have an overheating engine…this could mean you have no coolant in the engine, or not enough coolant.

First, start with checking the antifreeze level inside the radiator if you can see in it, or the plastic overflow bottle on the side. Is it low…very low? Go ahead and fill it up with just plain tap water from your garden hose for now.

Start the engine and let it warm up to normal temp, does the heater blow hot air now?  Can you see any of the water leaking from under the hood anywhere?  I would also pull back the carpet from the passenger side interior space up under the dash. Is the carpet damp or wet? That could be due to a leak in the heater core and leaking coolant inside the vehicle.

If the coolant inside the radiator is full and you did not have to add any, or not much anyway then I would look at the thermostat. Follow the upper radiator hose to where it connects to the engine. The thermostat housing is what the hose attaches to. Is the upper hose hot now that the engine is at normal temp, it should be.

If the upper hose is hot, then feel the lower radiator hose, it should be about the same temp.  If it is, then feel the two smaller rubber hoses going to the heater core. They should be going from the engine to the passenger side of the vehicle…find em?  They both should be hot as well.

If one heater hose is cold and the other is hot, then a problem inside the heater core inside the dash is probably the culprit.

If neither heater hose is hot, then we still have a restriction somewhere under the hood, an air pocket trapped inside the system,and it needs to be bled out or you have a low coolant condition and the engine needs more coolant.

What I would recommend you do now is to visit a mechanic and have them do a cooling system pressure test. This test adds air pressure inside the radiator and helps you locate coolant leaks. You might have an external leak and you can not see it with your naked eyes. You also might have an internal coolant leak inside the engine like a head gasket causing the overheating.

Now, if the upper radiator hose is hot but the lower hose and the heater hoses are cold then try a new thermostat and see if the issue is repaired or not.  The thermostat should open and close as the engine temp moves up. If the thermostat is “stuck” it can close off all coolant to the engine…thus overheating and no heater heat will result.

Please share this with your friends,

Austin Davis